With ever increasing pressure from automotive consumers, flexibility and adaptivity in the design of vehicle structural components are increasingly required in order to provide a vehicle adapted to meet the broad customer demand. Further, with increased social awareness of a vehicle's impact on the environment, there is an increasing demand to minimize the overall mass of the vehicle while still meeting the feature requirements of the consumer. By reducing the mass of the structural components of the vehicle, several goals can be achieved. First, the overall weight of the vehicle can be minimized, thereby reducing the power and fuel required to operate the vehicle. Secondly, reduction of the mass of the structural components allows for the optimization of the interior volume of the vehicle, increasing occupant comfort and vehicle storage capacity.
The need for reductions in the weight of structural components in vehicles has led to a more efficient use of engineered materials having very high stiffness properties. Various types of engineered materials have been proposed to handle this ever-increasing desire for a reduction in weight of the structural components of the vehicle. Injection-molded and compression-molded technologies for large automotive body parts have provided processing platforms for the development of these structural components. Inherent in the large size of the automotive body parts is a requirement of high resin flow during the molding process. These high resin flows very often lead to an often unpredictable and unacceptable anisotropy within the molded components.
The localized anisotropy, which often occurs when large composite material parts are molded by injection or compression molding, may lead to significant variations or deviations in localized material properties. The flow of the matrix material during the molding process often causes alignment of reinforcement particles which often having a high modulus and high aspect ratio. These reinforcement particles are incorporated in order to provide strength and modulus enhancements to a composite part. Anisotropic mechanical properties manifest themselves in performance of the parts by causing inferior strength and modulus in directions orthogonal or perpendicular to the flow-induced alignment. Anisotropic physical properties, such as coefficient of thermal expansion, manifests itself into warpage of the part, causing non-uniform shrinkage upon cooling after molding.
Flow induced anisotropy can be avoided by using reinforcements having aspect ratios approaching one, such as spheroids. This approach however does not provide the strength enhancement needed to meet mechanical and performance requirements of structural vehicle components. Further, it is also possible to employ the use of reinforcement particles that have physical and mechanical properties that match those of the matrix. This approach, however, provides little or no enhancement of the mechanical properties of the composite structure.
A need, therefore, exists for a reinforced composite material for very large automotive components, such as vehicle body panels, vehicle frames or truck beds, that possess a very high stiffness and yet has of sufficient fatigue strength to maintain a vehicle body component over the life span of a vehicle. A need also exists for large injection molded or compression molded vehicle body parts having close to isotropic material properties to avoid post-molding deformation during cooling and inferior structural performance during use.